1. Field of the Invention
The invention relates to a projection-type liquid crystal display apparatus including a photoconductive-type liquid crystal light valve ("PLCLV" hereinafter) for reflecting an incident light flux and providing an image to the reflected light flux and a projecting lens for projecting the reflected light flux.
2. Description of Prior Art
FIG. 1 shows the construction of a PLCLV 1. A liquid crystal layer 11 is defined by a spacer 12 and orientation layers 13 and 14. A photoconductive layer 15 on which an image is drawn is laminated on the writing side of the orientation layer 14 through a reflecting layer 16 and a light shielding layer 17. A transparent electrode 18 is arranged on the surface of the reading side of the orientation layer 13. A transparent electrode 19 is arranged on the surface of the writing side of the photoconductive layer 15. The liquid crystal layer 11, the reflecting layer 16, the light shielding layer 17, the photoconductive layer 15 and the like are sandwiched by a pair of glass substrates 20 and 21 with the transparent electrodes 18 and 19.
The reflecting layer 16 reflects a projection light which enters from the reading side on which the liquid crystal layer 11 is located. The light shielding layer 17 absorbs the leakage light of the projection light from the reflecting layer 16.
In case that an AC voltage is applied across the transparent electrodes 18 and 19 in the PLCLV 1, when a CRT draws an image onto the photoconductive layer 15 so that the write light flux enters from the right side (writing side) in FIG. 1, an internal resistance of the photoconductive layer 15 changes in a manner that it decreases locally in accordance with the light and shadow portions (change in amount of the received light) of the image. The AC voltage between the transparent electrodes 18 and 19, consequently, is applied to the inside of the adjacent liquid crystal layer 11 corresponding to the distribution of the changed internal resistance of the photoconductive layer 15. As a consequence, birefringence occurs due to spatial modulation of liquid crystal molecules in the liquid crystal layer in accordance with the potential distribution of the photoconductive layer 15, so that a light and shade pattern of a projection image to be projected to a screen is formed in the liquid crystal layer 11.
It is required that the black thin film of the light shielding layer 17 has both a shielding property preventing the leakage of a high power projection light flux emitted by a light source from passing and entering the photoconductive layer 15, and a resistance property with a high impedance absolute value to suppress an unwanted expansion of the potential distribution and maintain a resolution. However, it is difficult that these shielding and resistance characteristics are satisfied by only one single light shielding layer.